1. Field of the Invention
The field of art to which the invention pertains includes the field of fluid handling, electrohydraulic servovalves and failure detection thereof.
2. Description of the Prior Art
In the prior art it is common to use electrohydraulic servomechanisms to establish predetermined positions of control surfaces, engines and the like, responsive to electrical signals. It is desirous in such applications to detect failures of the servomechanisms to preclude catastrophic damage to the devices being controlled. The most objectionable types of failures occurring in a servosystem constitute the "hard-over" failure, for example, a constant saturated input signal pressure. When such failures occur the output member of the servomechanism moves to an extreme end of its travel. Obviously, such failures, if not immediately detected and corrective action taken, can lead to total loss of the overall system and failure of the mission in which the system is involved, particularly where aerospace vehicles are concerned. The most difficult to detect are usually the "soft" failures such as loss of input signal or loss of fluid pressure.
In the prior art various schemes have been developed to detect failures in the servomechanisms and responsive thereto to provide signals or actuate disenabling mechanisms. The best prior art known to applicants is contained in U.S. Pat. Nos. 2,886,009, 2,995,014, 3,265,089 and 3,552,433 and 4,054,154. Although such prior art systems operate appropriately under the applications and circumstances for which they were developed, they, for the most part, require conversion of position to pressure to electrical signals or similar such conversion, thereby requiring additional components as well as time to accomplish the detection signalling and/or disenabling.